PITTSBURGH — Willie Parker and Troy Polamalu practiced Wednesday and expect to play Sunday against the Cleveland Browns, but it’ll be a 2-for-1 deal since Aaron Smith was placed on injured reserve late Tuesday afternoon.

The last time Smith missed a significant portion of playing time was 2007, when the Steelers’ left defensive end suffered two different injuries and missed six full games and all but one series of a seventh.

The Steelers went 3-4 in those games and allowed 4.8 rushing yards per carry. They allowed 3.4 per carry with Smith in the lineup that season.

Polamalu called Smith “irreplaceable,” and said, “I honestly believe that our defensive line controls the outcome of the game. It hurts us. But there are guys who are going to be able to step up and hopefully play as well as he did.”

That’s the sentiment in the Steelers’ locker room because replacements Travis Kirschke and Nick Eason believe they’re better players than they were in 2007, and first-round pick Ziggy Hood, while raw, brings size and speed in reserve.

The Steelers can also use nose tackle Casey Hampton in the pass-downs packages, as they did Sunday when Smith missed the fourth quarter in Detroit. Backup nose tackle Chris Hoke can also slide over to play end in an emergency. The Steelers also signed sixth-round pick Sunny Harris back off the Carolina practice squad Tuesday evening.

So there are enough bodies, which left Polamalu feeling more optimistic.

“Last time he was out, I don’t think it was all that bad,” Polamalu said.

“I don’t think we won that many games, but I don’t think it was that position that was at fault. Guys like Travis and Nick and Ziggy are going to be able to step up, and I’m sure they’ll do as good of a job.”

Kirschke will start in Smith’s place. He admitted that he’s better on the right side, but has grown more comfortable playing the left, where he was put as Smith’s injury (right rotator cuff) worsened during the past few weeks.

The 35-year-old Kirschke hasn’t missed a game since joining the Steelers in 2004, but he’s fought through plenty of back pain during that time. He missed Wednesday’s practice after the back acted up on him Sunday and Monday, but he said Tuesday that he felt much better.

Eason, 29, joined the Steelers in 2007 and started for Smith eight weeks later. He said he’s a better player today than he was then.

“You guys watch the game. This is not some 1-2-3 defense here. It’s pretty complicated,” he said. “There are a lot of different things you have to know, audibles and adjustments you have to make. Coming in my first year, I was basically thrown in the fire and learned the defense. It was not difficult, but it took me some time to get all the nicks and nacks. But now I’ve been here two more years. Even the next year I could tell the difference in my game, with more confidence in knowing what I was doing. Any time you can have more confidence in knowing the defense, you can play faster. So, yeah, I’m totally a better player than I was two years ago. I’m looking forward to getting the opportunity to play.”

As for Hood, the rookie agreed with the assessment of his head coach, who told reporters Tuesday that Hood wasn’t ready to step in as the starter.

“Overall, everything’s been hard because I’ve had to go from an attack defense (at the University of Missouri) to a 3-4,” Hood said while standing next to Smith’s empty locker stall.

Clearly, the Steelers had mentorship in mind with their floor design.

“He’s been a great guy,” Hood said. “Everything from my stance to getting off and shedding blocks I learned from him. Everything. I watch him and I try to study him as much I can.”

Smith struggled through Sunday’s game just as he’d struggled the past couple of weeks with the injury, the same injury Hines Ward played with last season. Ward risked cutting short his career while playing, but finished the season and underwent surgery a week after the Super Bowl.

“I tore mine the second game when we were up in Cleveland,” Ward said. “And every day, when (Smith) would get here, he’d say ‘How in the world did you play?’ But the difference with me playing wide receiver and him playing the interior line is he has to use his shoulder each and every play, so you had to look at Aaron’s health for the future more than anything.

“Putting him on IR was definitely a blow to our defense, but that’s why Kevin (Colbert) and Coach (Mike) Tomlin put together a 53-man roster to go into the season. Over the course of 16 games, we’re going to lose a player here and there. Coach Tomlin always says we don’t have backups, we have starters in waiting.”